The 21-year-old has already scored two goals in ten Premier League matches for Chelsea

However, there were fears that Chelsea had broken FIFA rules by playing Traore in that fixture against the Gunners.

Fifa regulations do not allow the international transfer of players under 18. But both clubs were adamant the fixture had been a friendly and Traore was, at that stage, still a trialist.

Despite signing pro terms with the west Londoners Traore could not play for the Blues’ first team as he did not have a work permit.

Bertrand Traore success at Ajax means Chelsea has a lot to look forward to on his return to the club

Mourinho had no concerns over the future of the young forward, though, and said at the time: “Now we want to keep him. We have to wait until he becomes 18 to try to get a permit for him to stay in England.

“It’s the rules and we have to accept them. He plays for his national team. Sooner or later the committee has to give him a permit to play in England.”

In the meantime he headed to Vitesse Arnhem, one of Chelsea’s sister clubs, and scored three times in seven Eredivisie starts before the end of the campaign.

That was enough for all parties to agree to an extension of the loan deal which would see Traore remain in the Netherlands for the 2014/15 campaign.

Bertrand Traore will be hoping his form will help him to be given a chance by Antonio Conte next season

Traore was impressive again and finished his first full season in European football with 17 goals in all competitions.

By this point Mourinho had seen enough. When Traore reported for pre-season in the summer of 2015 he was given the number 14 jersey vacated by Andre Schurrle and included in the first-team squad for the new season.

Traore made his Blues debut in the Champions League, coming on as a substitute against Maccabi Tel Aviv in a 4-0 group stage victory at Stamford Bridge.

He had to wait until December for his Premier League bow – again as a substitute – in a shock 1-0 home defeat against Bournemouth.

Friday Premier League match preview including Chelsea v West Brom

The following month Traore scored his first senior goal for the club in a 5-1 rout of MK Dons in the FA Cup at Stamford Bridge. He finished his maiden campaign as a first-team player with four goals in 15 appearances across all competitions.

But the £33million signing of Michy Batshuayi, coupled with Diego Costa’s return to form, meant chances at Chelsea would be limited this season and Traore joined Ajax on loan for the 2016/17 campaign.

Handed the number nine shirt, Traore did not get off to the best start at the Johan Cruyff Arena and had to wait until his sixth league appearance, against PEC Zwolle, to open his account.